1. Field of the Invention
The present invention relates to an apparatus and method for topographic processing. In topographic processing, map data of one or more maps is analyzed to derive a suitable result, such as a display therefrom. For example, a relief map of a geographical area, formed from map data including contour data, may be displayed.
2. Summary of the Prior Art
It is known to store data representing a map in a computer, and then generate a display of that map. In general, the map data is stored as point data and the operation of generating the display of the map includes joining the point data by lines. However, for the sake of convenience of discussion, those lines will be considered as included within the map data itself.
If the computer memory is sufficiently large, it can store maps representing the same area or region at different scales. In that case, a map of larger scale will display more than a map of smaller scale. Thus, for example, a map of small scale may show only major roads, rivers, and other geographical objects, while a map of larger scale may show minor roads, streams, and a wider range of geographical items. If this were not done, and the small scale map made use of, and displayed, the same data as the large scale map, then either the small scale map would be excessively cluttered with objects, or the large scale map would not give an accurate representation of the region displayed.
It is also known for the user to select the map to be displayed in dependence on the information needed by the user. An example of this is shown in JP-A-63-98780. In that disclosure, the user selected a magnification from a reference scale, and the system then selected a map whose scale was closest to that determined by the magnification, and displayed that selected map. In JP-A-63-98780, there was no processing of the map data, except to display it.
Since such a system contained map data representing maps of different scales, it is also possible to simultaneously display parts of a region at one scale, and other parts at another scale. An example of this is shown in JP-A-2-61690, which was concerned with a display system for a vehicle. In JP-A-2-61690, the region immediately adjacent the vehicle was displayed at a large scale, and more distant regions displayed at a small scale. There was also an intermediate region between the two scales of lines formed by joining points on the edges of the two regions. Again, however, the system only displayed a map, although a composite one.
An alternative proposal, in JP-A-61-267778 was to have two maps of the same scale displaying different data, with one map being based on more data and thereby showing more geographical items. Then, for vehicle navigation, the area immediately adjacent the vehicle was displayed using the map with more geographical items, and regions further from the vehicle were displayed using the map with less geographical items, to give a clear. Again, only map data was displayed.